Chapter 13

Question 1

Producers

Answer 1

Photosynthetic organisms that manufacture organic substances using light energy, water, carbon dioxide, and mineral ions.

Question 2

Saprobionts

Answer 2

Decomposers, a group of organisms (mostly fungi and bacteria) that break down complex materials in dead organisms into simple ones. This releases valuabe materials in a form that can be absorbed by plants

Question 3

Food chain

Answer 3

Describes the feeding relationship between producers and consumers. Each stage in a chain is a trophic level and the arrows represent the direction of energy flow.

Question 4

Food web

Answer 4

The food chains present in a habitat showing how they overlap.

Question 5

Biomass

Answer 5

The total mass of living material in specific area at a given time. Measured in g m -2 or g m -3 (if in a pond or an ocean)

Question 6

Calorimetry

Answer 6

Measures the energy store in dry mass. Dry material is weighed and then burned in pure oxygen within a sealed container (a bomb). The bomb is surrounded by water and the heat of combustion causes a small measurable temperature change.

Question 7

Gross primary production

Answer 7

The total quantity of chemical energy store in plant biomass.

Question 8

Net primary prduction

Answer 8

Plants use 20 - 50% of GPP for respiration. NPP is when these respiratory losses have been taken into account

Question 9

Why is most of the sun’s energy not converted to organic matter?

Answer 9

• Over 90% is reflected back by clouds and dust or absorbed by the atmosphere.
• Not all wavelengths of light can be absorbed by plant photosystems and used for respiration.
• Light may not fall on the chlorophyll molecule
• Other factors may limit photosynthesis

Question 10

Why is there a low transfer of energy between each level?

Answer 10

• Some of the organism is not consumed
• Some of the organism is not digested.
• Some energy is lost in urine and faeces
• Lots of energy is lost to the environment from respiration

Question 11

Name three things caused by the inefficiency of energy transfer between organisms?

Answer 11

• Most food chains only have 4 or 5 trophic levels as larger breeding populations can not be supported.
• The biomass decreases with each trophic level
• The total amount of energy available is less at each trophic level

Question 12

How does factory farming increase the energy conversion rate?

Answer 12

• Movement is restricted so less energy is used for muscle contraction.
• The environment can be kept warm so less energy is lost as heat
• Feeding can be controlled so optimum amount of food is cosumed minimising wastage.
• Predators can be excluded so no loss to other organsims in the food web

Question 13

How do plants acquire nitrogen?

Answer 13

Plants take up nitrate ions by their roots from the soil by active transport

Question 14

Ammonification?

Answer 14

The production of ammonia from organic nitrogen containing compounds (urea, proteins, nucleic acids and vtamins). Saprobionts feed on faeces and dead organisms releasing ammonia which then forms ammoium ions in the soil.

Question 15

Nitrification

Answer 15

Conversion of ammomium ions to nitrite ions (nitrosomonas) and nitrate ions (nitrobacter) in oxidation reactions. Carried out in aerobic conditions.

Question 16

Denitrification

Answer 16

When soils have anaerobic conditions there is an increase in denitrifying bacteria these convert soil nitrates into nitrogen, reducing the availabilty of nitrogen containing compounds for plants.

Question 17

Nitrogen fixation

Answer 17

Nitrogen is coverted to nitrogen containing compounds, can be carried out industrially and naturally when lightning passes through the atmosphere.

Question 18

Free living nitrogen fixing bacteria

Answer 18

Reduces nitrogen to ammonia which they then use to manufacture amino acids. Nitrogen rich compounds are realeased from them when they die and decay.

Question 19

Mutualistic nitrogen fixing bacteria

Answer 19

Live in nodules of legumous plants. They obtain carbohydrates from the plants and the plants obtain amino acids from the bacteria.

Question 20

Why is the phosphorus cycle so important?

Answer 20

It is a component of ATP, phospholipids and nucleic acids

Question 21

What is the main resevoir of phosphorus in the P cycle?

Answer 21

Mineral form- there is no gaseous phase

Question 22

Describe the phosphorus cycle?

Answer 22

1. Weathering and erosion of sedimentary rocks dissolve phosphate ions for absorbtion by plants .
2. Feeding and digestion of plants by animals passes on these phosphate ions.
3. Excretion and decomposition of excess phosphate accumulate in waste material eg guano, slurry, bone
4. Saprobionts deompose dead plants and animals releasing their phosphate into water or soil.
5. Deposition of the phosphate ions transport them by streams and rivers into lakes and oceans where they form sedimentary rocks.

Question 23

What role do mycorrhizae play in nutrient cycles?

Answer 23

• They are associations between certain types of fungi and the roots of plants.
• They act like extensions of the plants root systems, increasing the surface area of the root system for absorbtion of water and mineral ions.
• They act like a sponge holding water and minerals close to the plants.
• Enabling better resistance against drought .